Near-infrared light can penetrate skin – meaning it can trigger fluorescent molecules circulating in the blood, and this fluorescence can be picked up by an external monitoring device. If the molecule’s fluorescence changes in response to chemical conditions, these changes can also be detected, and you have a sensor.

But fluorescent dyes can be toxic, and they’re quickly filtered out of the body. “The solution we found: encapsulate the sensors in red blood cells,” Shao explains. “In this way the sensors can remain in the body and be protected from the immune response.”

They began with a pH sensor.

They placed red blood cells in a solution that causes them to swell. This opens up a pore in the cell.

If the solution also contains the fluorescent dye, some of this dye will be exchanged with some of the contents of the red blood cell.

The red blood cell can then be resealed and injected back into a patient for monitoring for up to 3 months.

The new sensor cells replace a series of invasive blood samples with a one-time injection. And anything in the blood that can enter the red blood cell can, in theory, be detected using the right dye. This includes glucose.

Janet Fang has written for Nature, Discover and the Point Reyes Light. She is currently a lab technician at Lamont-Doherty Earth Observatory. She holds degrees from the University of California, Berkeley and Columbia University. She is based in New York.
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